1. Field of the Invention
The present invention relates to an optical data recording and reproducing apparatus (i.e., an optical disc apparatus) which records and reproduces optical data onto and from a recording medium, such as an optical disc or a photomagnetic disc. More precisely, it relates to an optical head (i.e., a carriage) which is moved across data recording tracks which lie in the circumferential direction of the optical disc.
2. Description of Related Art
Generally speaking, an optical disc apparatus has a carriage which is movable in the radial direction of the optical disc and which holds a reflecting mirror thereon for reflecting light (i.e., a laser) emitted from a stationary optical system in the radial direction of the optical disc towards an objective lens, which is held by a lens holder. The objective lens is supported on the lens holder by a holding flange which is provided on the outer circumference of the objective lens and perpendicular to the optical axis thereof, and an annular supporting surface which is provided on the lens holder to support the holding flange of the objective lens. The annular supporting surface of the lens holder has a center circular opening where the objective lens is placed. However, in known supporting mechanisms as mentioned above, the holding flange of the objective lens and the annular supporting surface of the lens holder are made flat, the flat surfaces being perpendicular with respect to the optical axis (i.e., the design optical axis). Accordingly, the position of the objective lens can be adjusted only in a direction perpendicular to the optical axis within a limit defined by the difference in diameter between center circular opening of the lens holder and the objective lens.
Due to the possibility in a manufacturing error of the lens holder or carriage, the annular supporting surface of the lens holder may not be normal to the design optical axis. There is a further possibility that the optical axis of the objective lens may be inclined or deviated from the design optical axis due to a manufacturing error of the holding flange of the objective lens.
To correct the inclination or deviation of the optical axis of the objective lens with respect to the design optical axis, the lens holder or carriage is usually provided with an adjusting mechanism. However, such an adjusting mechanism is bulky and complex in construction, resulting in a heavy and complicated movable optical system, as a whole.